Age-related changes in the dorsal skin histology in Mini and Wistar rats.

Mini rats (Jcl: WistarTGN(ARGHGEN)1Nts (MRs) are Wistar rat (WR)-derived transgenic rats in which the expression of growth hormone (GH) gene is suppressed by the presence of antisense transgene. The plasma GH level of MRs is reduced to 40 to 60% of that of WRs. In this study, to evaluate the influence of GH deficiency on the skin nature, age-related changes in the dorsal skin histology were compared between male MRs and WRs. Although there were no essential differences in the skin structures between the two strains, MRs had thinner skin with less collagens, more abundant subcutaneous adipose tissues and small-sized sebaceous glands compared with WRs. On the other hand, the hair cycle evaluated by the morphology and the depth of hair follicles was greatly different between them. Namely, two cycles of 4 weeks each were observed in both strains during the first 8 weeks after birth, but the cycle entered a long-lasting quiescence (telogen phase) in MRs while the 3rd cycle started in WRs afterwards. The lower level of serum insulin-like growth factor (IGF)-1 in MRs may be related to such a difference in hair cycle pattern, although the levels of IGF-1 and IGF-1 receptor mRNAs in the dorsal skin tissues were similar between MRs and WRs. MRs are considered to be a useful animal model for dermatopathy in patients suffering from GH deficiency and for grasping a clue to elucidate the exact effects of GH on the skin nature, especially on hair follicle development.